The combustion of diesel fuel in internal combustion diesel engines is accompanied by problems accentuated at cold temperatures associated with the special characteristics of the diesel fuel. At very cold temperatures the wax constituents of diesel fuel tend to congeal and water and other contaminants may crystallize particularly in the diesel fuel filter which presents extended surface areas to cold air. The diesel engine may therefore stall or refuse to start as a result of a clogged fuel filter or other fuel passageway. Furthermore, the interference in effiency of combustion by water and other contaminants in the diesel fuel increases with lower temperatures.
As a result of these problems of loss of power, stalling, and failure to start associated with diesel engines in cold weather, a variety of "in-line" diesel fuel heaters have been developed and are available on the market for heating diesel fuel before it passes to the diesel fuel filter. Such heaters generally comprise a separate appliance or piece of equipment permanently installed with some difficulty in a crowded engine compartment and may require intervention with special modifications, fittings and connectors in the fuel line itself. Each intervention or connection in the fuel line presents another vulnerable source of contamination, leakage, or air in the fuel system. For example, the Davis U.S. Pat. No. 4,368,716 and the Wagner U.S. Pat. No. 4,349,001 illustrate examples in which a separate fuel preheater and processor is introduced into the diesel fuel line at a different location from the fuel filter.
The closest prior art of which applicant is aware consists of the Baker U.S. Pat. No. 4,372,260, the Dushane U.S. Pat. No. 2,348,247, and the Lamb U.S. Pat. No. 2,331,482, all of which describe oil and fuel preheaters in the form of a hot water jacket formed or installed in the vicinity of the fuel filter although not directly around the filter. In each case the hot water jacket constitutes a rigid piece of hardware which is permanently mounted and installed adjacent to the fuel filter. Such examples require permanent installation of hardware equipment and do not themselves protect the extended surface areas of the fuel filter from cold air.